Some hangman at Tyburn smart (5)
I believe the answer is:
natty
'smart' is the definition.
(I've seen this before)
'some hangman at tyburn' is the wordplay.
'some' says the answer is hidden in the clue (some parts of the word are used).
'NATTY' can be found hidden inside 'hangman at tyburn'.
(Other definitions for natty that I've seen before include "Dapper (colloq.)" , "Smart, spruce" , "Flashily smart" , "Stylishly dressed" , "Stylish" .)